Sludge formation in spark ignited internal combustion engines as well as in certain types of diesel engines (hereinafter engines) is caused by a number of factors including engine design, engine operating conditions, fuel and oil.
To determine the effects of different engine oils on sludge formation, both engine sequence testing in the lab, such as the Ford VE test, and field testing are used.
Field testing is a significantly less controllable test environment than the engine laboratory. However, with appropriate test design and coordination, all key test parameters can be reasonably controlled.
Heretofore, the usual test for determining the effects of different engine oils on sludge formation in engines involved determining the sludge ratings for the different oils after running the oils in substantially identical engines for 60,000 miles or more under controlled operating conditions that included changing the oil and filter in each engine at predetermined intervals. The major drawback to these standard field tests is that they take a relatively long period of time to complete. Also, most engine lubricant formulations used today are of SG/CC or better quality, which will not normally produce any significant sludge accumulations in engines during these standard long-term field tests.